IgG, IgE, IgD
C H A P T E R 3 5 , F IG U R E 11
Immunoglobulin classes. The five immunoglobulin classes are determined by the
amino acid sequences of the constant regions of the heavy polypeptide chains (see Table 35-2).
Equivalence of antigen and antibody
C H A P T E R 3 5 , F IG U R E 1 2
Antigen-antibody complex formation. Optimal concentrations of antibody and anti-
gen result in cross-linking and precipitation of the antigen-antibody complexes. Cross-linking is important in B-cell
stimulation when antigens bind to the IgM B-cell receptors. If antibody is present in excess, then all of the epitopes
on the antigen can be occupied by single antibody molecules (subject to steric exclusion) and the antigen-antibody
complexes do not precipitate. If antigen is present in excess, then all antibody binding sites can be occupied by anti-
gen molecules and no cross-linking occurs.